The present invention relates to wireless telecommunications networks, in particular wireless local access networks (WLAN) conforming to the IEEE 802.11 family of standards.
Such networks are also known as Wi-Fi networks. In many applications they are used to network stations (for example computers, personal digital assistants, and peripherals).
In the document “IEEE 802.11a-1999, IEEE 802.11b-1999, IEEE 802.11d-2001, Part 11: wireless LAN medium access control (MAC) and physical layer (PHY) specifications” the 802.11 standard defines a wireless network traffic regulation method that uses a system of congestion windows (CW) to regulate traffic. According to that standard, in order to determine the time at which to send a data packet, a station draws by chance a random number between 0 and CW−1, the value CW being an integer between two values CWmin and CWmax specified by the 802.11 standard.
This value CW is counted down to send the packet, the countdown being delayed if the station determines that another station is in the process of sending. Unfortunately, that system using congestion windows causes a large number of collisions in the wireless network, which from the user's point of view are reflected in a great loss of bandwidth.
The document by Z. Abichar and M. Chang, “CONTI: Constant Time Contention Resolution for WLAN Access”, IFIP Networking 2005, below referred to as [CONTI], proposes a constant time contention resolution method that uses a series of successive very short tests to select the station that is going to send.
According to the CONTI method, stations seeking to send are eliminated using a try-bit Boolean variable. To be more precise, each station chooses this variable randomly and sends a signal over the network if the random value is equal to 1, or if not listens to the network. A station withdraws from the network, i.e. decides not to send its data packet during a series of selection rounds, if the binary value is equal to 0 and it detects a signal sent by the other stations.
Although offering better performance than the congestion method defined by the 802.11 standard, the proposed CONTI contention resolution method still causes a high number of collisions in the wireless access network, of the order of 5%.
That problem is caused by the fact that the law of probabilities used for drawing the try-bit random variable is not optimized.